1. Field of the Invention
The invention relates to organosilicon compounds, to processes for producing them, to their use for producing hydrophilic surfaces, and to silicone elastomers with hydrophilic surfaces. In particular, the invention relates to compounds which, when added to curable mixtures, provide, after curing, a hydrophilic surface, or which can be applied after curing to the surface of the silicone elastomers, in which case they are anchored to the surface and thereby give the silicone elastomers a hydrophilic surface.
2. Description of the Related Art
Polydimethylsiloxane elastomers are, depending on the formulation, soft, very flexible materials with a series of advantageous properties such as extraordinary thermal and electric stability, high optical transparency, good gas permeability and high elasticity, even at very low temperatures. The high hydrophobicity of these elastomers is also often advantageous for applications where water repellency is desired. However, the low surface energy which polydimethylsiloxane surfaces exhibit can also be disadvantageous, particularly if biological units absorb at the surface. For example, the hydrophobicity, i.e. poor wettability of the surface of polydimethylsiloxanes is responsible for the surfaces becoming susceptible to so-called “fouling” by proteins or lipids. Organisms are able, with surprising stubbornness, to adhere to silicone surfaces and then to multiply.
By contrast, biological molecules and organisms exhibit a considerably less efficient adherence to certain types of hydrophilic surfaces. For example, poly(ethylene glycol) (PEG)-modified surfaces are known for repelling proteins and reducing cell adhesion. Other strategies such as the anchoring of polysaccharides, proteins and surface-active molecules likewise reduce the tendency of polymer surfaces towards fouling.
Primarily two strategies have been pursued in order to enhance the hydrophilicity of silicone surfaces. The first involves oxygen plasma treatment, UV irradiation and corona discharge, with superficial OH groups being produced in all methods. One disadvantage of this procedure is that the surface can become damaged as a result, as well as expenditure on apparatus which is required to implement this treatment. Alternatively, hydrophilic materials can be absorbed on the surface, bound to the surface (e.g. poly(ethylene glycol)) or be incorporated into the material by copolymerization. All these strategies have disadvantages. Silicone polymers have high mobility and exhibit surface reversion, during which the hydrophilic materials again end up underneath the mobile silicone polymers since the latter migrate with the interface to the air. Although silicone elastomer surfaces can be made hydrophilic such that even contact angles of 0° are achieved, the hydrophobicity of the surfaces is generally regenerated within a short time.
In order to overcome this problem, it was proposed in WO-A 11022827 to bond allyl-modified polyethylene glycols of the structure
onto silicone surfaces by addition onto superficial Si—H groups by means of hydrosilylation. At a comparatively high concentration of these groups on the surface, contact angles of less than 10° could thus be achieved. However, these compounds are subject to a hydrolytic cleavage of the trisiloxane group, whereupon the hydrophilicity of the surface is as a result significantly reduced again over the course of time. Moreover, these compounds are only suitable for modifying Si—H-containing surfaces.